The invention concerns a pulsator for milking machines, comprising a bolt traveling back and forth in a housing and activating a slide that alternately connects the pulsator's outlets to a source of vacuum and to the atmosphere, a diaphragm accommodated in a chamber at each end of the slide and moving the bolt back and forth, and an alternator triggered by the slide as it arrives at one end or the other of its stroke and connecting the chambers back and forth and alternately to the source of vacuum and to the atmosphere.
Such an alternating pulsator is known from German 3 702 419 C1. It alternately connects the channels between pairs of teat cups in a milking machine to a source of vacuum and to the atmosphere. The channels are connected to the source of vacuum during what is called a suction phase. How long this phase lasts can be varied by varying the pulsator's rate.
The speed at which the bolt travels back and forth in the housing, however, can vary due to unavoidable manufacturing tolerances. The lengths of time vacuum and atmospheric pressure are supplied to the channels between the pairs of teat cups from the chambers inside the pulsator will also accordingly vary. This irregularity in the operations of known pulsators is called stagger.
The stagger in known pulsators is suppressed by means of varying the capacity of at least one of the chambers accommodated therein.
The capacity of the chambers directly affects the timing of compression and decompression therein. These procedures will be more rapid in smaller chambers. Reducing the capacity of the chambers will accordingly accelerate the bolt, increasing the rate of pulsation, and abbreviating the suction phases. If the capacity of only one chamber is reduced, only the suction phase in the same half of the pulsator will be abbreviated, suppressing the stagger.
The means of varying capacity in the known pulsator either complicate the mechanism considerably or allow only discontinuous stagger suppression.
Another pulsator is known from WIPO 8 902 216 A1. Stagger is suppressed by means that shift the extreme positions of a valve in relation to vacuum and atmosphere channels associated with it in the direction of the slide's stroke but without varying the length of the stroke. This type of control, however, is not practical for pulsators wherein the position of the slide in relation to the channels is dictated by additional apertures activated by the slide at the end of each stroke and accordingly activating the alternator, which then shifts the chambers back and forth between vacuum and atmospheric pressure. The slide does not change direction until one of the apertures is aligned with a chamber associated with it on the slide.